Process for sweetening hydrocarbon distillate



C. D. LOWRY, JR

Filed May 51, 1939 Af.. nw

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Jan. 2o, 1942.

` PROCESS FOR SWEETENING HYDROCARBON DISTILLATE N @Nl' www QLYNNR www Patented Jan. 20, 1942 PROCESS FOR SWEETENING HYDROf CARBN DISTILLATE Charles Donk Lowry. Jr., Chicago, lull., assigner to Universal Oil Products Company, Chicago, lll., a corporation of Delaware Application May 31, 1939, Serial No. 276,606

e claims. (ci. 19e-ss) This invention relates to a method for'sweetening petroleum distillates and more particularly, to an improvement in the sodium plumbite or doctor sweetening process.

lThe process is especially concerned with the treatment of petroleum distillates of motor fuel boiling range, although corresponding hydrocarbon distillates from other sources and those of higher boiling range may also be included within the scope of the invention. Such oils may include kerosene distillates, furnace oils and the like, from petroleum or other hydrocarbon sources.

Practically al1 hydrocarbon distillates and especially those of motor fuel boiling range require some form of treatment before they are marketable. In recent years many distillates including both straight-run and cracked products have received only a sweetening treatment prior to being marketed. Cracked products especially require additional stabilization to prevent the formation of undesirable gums, color, and oxidation products during the storage period, this being achieved by the addition of small amounts of gum inhibitors. In nearly all cases both straight-run and cracked gasolines require sweetening even though no other treatment is used. The most widely used process for this purpose is the so-called sodium plumbite or doctor process which involves contacting the gasoline with a solution of litharge in sodium hydroxide and subsequently adding a suiicient quantity of elementary sulfur to bring about the conversionA of the lead mercaptides formed to soluble disulfides and insoluble lead sulfide.

' As usually practiced this process has a number of disadvantages among which is the need for using execessive quantities of elementary sulfur in order to obtain a satisfactory break, i. e., separation of the lead sulfide from the gasoline. 'I'he presence of this excess sulfur `during the reaction results in the formation of alkyl-polysulfides which are detrimental to the color and gum stability of the gasoline and also to the octane number and susceptibility to tetra-ethyl an alkaline plumbite solution thereby converting 5f".

In U. S. Patent No. 2,055,423 a` mercaptans present therein into lead mercaptides. separating the gasoline, blending therewith a further portion of the .sour gasoline, adding sumcient sulfur to the blend to decompose the lead mercaptides, washing with water which may or may not contain added alkaline substances,-

separating the sweet gasoline, recovering the lead sulfide from the aqueous layer, combining said lead sulfide with the residual plumbite solution used in the initial step, and regenerating said mixture.

. 'I'he accompanying drawing illustrates diagrammatically one embodiment of the process when sweetening gasoline. The invention should not be construed as limited to the exact apparatus described in the drawing. `The drawing has not been -made to scale nor has any attempt been made to show the various 'pieces of equipment in exact proportion.

Referring to the drawing, gasoline amounting to 30-70% of that produced is pumped through line I and valve 2 and combines with sodium plumbite solution of suilicient amount and concentration to be in excess of that required to react with the mercaptan sulfur present from line 3 and valve I. The mixture passes through pump 5, mixer 6, and valve 'I into settler 8. The residual doctor solution is withdrawn through line 9 and valve I0. 'I'he gasoline, free of doctor solution but containing lead mercaptides in solution, is mixed in line II with sour gasoline amounting to 'Y0-30% of that produced, entering through line I, line I2 and valve I3 and the two gasolines are thoroughly mixed in mixer I4. A minor portion of the gasoline is passed through line I5 and valve I6, through sulfur pot I1, valve I3 and line I9 which joins with line II and the mixture passes through mixer 20 and valve 2| into settler 22 where the reaction occurs. A portion of the mixture may be recirculated through line 23, line 24, valve 25, pump 25 and valve 21, and line I3. This is done in order to maintain the lead sulfide in suspension and to insure adequate time for reaction of the gasoline. Line 23' and valve 23" may be used for drawing on' samples. A portion of the gasoline is withdrawn through line 28, valve 29, pump 3d, and valve 3| lines 3 and 32' and valve 33' can be used byy passing into line 32. The suspension of lead sulfide. settles out in settler 35.y The clear, sweet gasoline is withdrawn to storage through line 36 and valve 31. The lead sulnde slurry is removed y through line 38 and valve I! to settler 40 where the water may be withdrawn through line 4I and valve 42. The lead sulfide settles into the bottom oi the cone-shaped vessel 4l and may be mixed with the residual doctor solution from settler l which enters through line l, valve I0, line 4l and valve 44. A part or all of the doctor solution may be passed through line 45 and valve 46 which joins with line 41. The slurry of lead sulilde is withdrawn through line 41 and valve 48 to a regeneration system not shown.

Although elementary sulfur is generally used for breaking out lead sulilde, in certain instances alkali metal polysulildes such as those ot sodium may be used. The general formula of this type compound is Nessun. limits of approximately 0.5-3. The polysulilde sulfur serves the same purpose as the elementary sulfur in this case but is not necessarily exactly equivalent thereto.

'I'he advantages of the present process are:

a. It oiers a convenient and practical method for separating and recovering the lead sulfide from the distillate being sweetened, thus facilitating its regeneration when this step is carried out.

b. When treating cracked gasoline the sweetened gasoline is substantially tree of alkaline doctor solution so that no chemicals are lost and no alkali is carried to the storage tanks and alkali-soluble inhibitors which are often used in the gasoline are not removed, since separation of reagents is more readily accomplished.

c. Little or no emulsion oi' distillate and lead sulde is formed, thus reducing losses.

d. The suspension of lead sulilde in water is readily separated for purposes of regeneration.

e. 'I'he lead suliide will contain occluded thereto little or no oil, thus increasing the ease of regeneration, said regeneration being accomplished in a separate step by means of air and steam at elevated temperatures.

- f. The process is an improvement over that of the above mentioned U. S. Patent No. 2,055,423 which proposes to contact the gasoline alter addition of the elementary sulfur with clay in order to remove the suspended lead suliide. This results in loss of chemical or at best must be followed by expensive methods for recovering the lead sulfide.

u. Gasolinesweetened by the present process has better color stability, octane number and susceptibility to tetraethyl lead than the same gasoline sweetened by the conventional doctor method. In the case of cracked gasolines the storage stability and the susceptibility to lnhibitors is improved to a marked extent.

The following example illustrates the usefull ness and practicability oi the process.

A cracked gasoline obtained from a blend oi' West Texas and Mid-Continent crude oils contained 0.06% of mercaptan sulfur.A It was sweetened by the present method in which 40 parts of the sour gasoline were contacted with approximately 8% by volume of 15 B. doctor solution, the gasoline separated, and 60 parts of sour gasoline were blended with the lead mercaptide-containing portion. Suillcient sulfur was added t cause the separation of the lead sullde. The gasoline was then contacted with water and separated. The results obtained by this method of treatment compared with a conventional doctor treatment are shown in the following table.

Conventional Process of Sweotening method doctor process present inventlon Color 20 Color stability, 2 hours sunlight Hazy 19 Doctor test Neg. Neg. Free sulfur. percent 0:016 0.002 Oxytgsau bomb induction period, min- Blank 110 13u C 10.0%?? commercilolnhibitor 230 300 op gum, mg.l cc.: Elink 185 135 i 0.008% commercial inhibl 30 15 Octane number. 09 70 Cc. tetraethyl lead/gallon to 78 octane number .1 00 l. 75 Copper strip corrosion 210 F Pos. N eg.

Usually n is within the The results show that the quantity of free sulfur remaining in the gasoline after sweetening by the present process is 0.002% as compared with 0.016% for the conventional doctor treatment. The gasoline sweetened by the present process had a longer induction period and lowe'r copper dish gum, both originally and after the addition of commercial inhibitor. The octane number was higher and a saving o! tetraethyl lead amounting to 0.25 cc. per gallon was realized. 'I'he copper strip corrosion test was negative as compared with a positive test for the con-l 'solution to convert mercaptans to lead mercaptides, separating unconsumed plumbite solution from the resultant mercaptide-containing distillate. combining with the latter additional sour distillate, adding sulfur to the mixture to convert the lead mercaptides to lead sultlde, and then washing the mixed distillates with water to separate the lead sulfide.

2. The process as defined in claim 1 further characterized in that the water employed in the washing of the sulfur-treated mixed distillates contains alkali metal hydroxide in solution.

3. A sweetening process which comprises treating sour hydrocarbon distillate with aqueous alkaline plumbite solution in excess of that required to convert mercaptans to lead mercaptides, separating the unconsumed aqueous alkaline plumbite solution from the mercaptide-containing distillate, combining with the latter additional sour hydrocarbon distillate, adding sulfur to the mixture to convert the lead mercaptides to lead sulfide, and then washing the mixed distillates with at least a portion of said unconsumed aqueous alkaline plumbite solution to separate the lead sulfide.

4. The process as dened in claim 1 further characterized in that said sulfur is added in the elementary form.

5. The process as dened in claim l further characterized in that said sulfur is added in the form of an alkali metal polysulflde.

6. 'I'he process as dellned in claim 1 further characterized in that the ratio of said mercaptide-containing distillate to said additional sour distillate combined therewith lies 'within the limits ot approximately 30:70 and 70:30.

CHARLES DOAK LOWRY, Jn. 

